Diesel combustion exhaust is a regulated emission. Various technologies have been developed for identifying and filtering out exhaust particulate matter (PM) before the exhaust is released to the atmosphere. Diesel particulate filters (DPF) are commonly used for particulate matter (PM) or soot control. The DPF may reduce the amount of PM emissions by trapping (or filtering) the PMs or soot in the exhaust. A particulate matter (PM) sensor located downstream of the DPF in the exhaust passage monitors the filtration efficiency of the DPF and is typically used for detecting leaks in the DPF.
The PM sensor operates by collecting exhaust particulates on a pair of metal electrodes separated by an insulating gap. When the PM sensor is exposed to particulates, the gap is bridged by electrically conductive material, yielding a change in resistance that is observed as an increase in current measured across the PM sensor electrodes. The time required for the current to rise to a threshold level depends on the amount of particulate matter to which the sensor is exposed (degree of leak in the DPF) and the design of the sensor.
One example approach to detect leaks in the DPF is shown by Yahata et. al. in U.S. Pat. No. 8,561,388. Therein, an estimating unit estimates a failure-state energization timing which determines the PM sensor current (or energization) assuming that the particulate filter has failed. Furthermore, a determining unit determines that the particulate filter is in a failure state when an actual energization timing of the PM sensor based on an output of the PM sensor is earlier than the failure-state energization timing estimated. Thus, by monitoring the energization timing of the PM sensor, the failure state of the DPF is determined.
However, the inventors herein have recognized potential issues with such systems. The leak detection described by Yahata et. al. may have issues particularly when lower DPF leaks are to be detected. As such, the actual energization timing of the PM sensor depends inversely on the leak rate of the DPF. In order to detect smaller leaks in the DPF, the energization timing may be longer than a single drive cycle, for example. However, longer timing is contradictory to OBD regulations which allow for only one drive cycle to complete necessary monitoring.
In one example, part of the issues described above may be addressed by a method comprising: adjusting engine operation in response to a particulate matter (PM) sensor coupled downstream of a particulate filter in an engine exhaust and indicating degradation of a particulate filter in the engine exhaust in response to a PM sensor performance within a single drive cycle and over a plurality of drive cycles. In this way, by monitoring the PM levels over a single drive cycle, larger leaks in the DPF may be detected. However if there are no large leaks in the DPF, the PM levels may be continued to be monitored for a longer duration, during the plurality of drive cycles, to detect smaller leaks in the DPF. In this way, larger and smaller leaks in the DPF may be monitored separately.
As one example, a faster leak detection may include indicating a large leak if the PM sensor current exceeds the threshold current within a single drive cycle. Thus, if the PM sensor current reaches threshold within a single drive cycle, then it may indicate that there is a large leak in the DPF, and appropriate mitigating actions may be initiated. However, if no leak is detected during the single drive cycle, a slower detection may be performed that includes monitoring the PM sensor current over multiple drive cycles. If the PM sensor current reaches threshold during one of the multiple drive cycles, then it may indicate that there is a smaller leak in the DPF, and corresponding mitigating actions may be initiated. However, if the PM sensor current stays below the threshold during all of the multiple drive cycles, then it may indicate that there is no leak in the DPF. In this way, by including separate detection methods for small and large leaks, DPF performance may be evaluated during multiple drive cycles.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.